Golf ball with heat resistant layer

ABSTRACT

A golf ball comprising of an outer core layer, or an inner cover layer having heat resistant properties to facilitate compression molding of a thermosetting polybutadiene-comprising layer over at least one thermoplastic layer. The ball comprises a thermoplastic inner core or core layer comprising of a low vicat highly neutralized ionomer material having a low melting point of less than 100° C., and a Shore C surface hardness of less than 80 and a compression of less than 70, wherein an outer adjacent thermoset layer is placed around the inner core or core layer, the thermoset layer comprising comprising a peroxide that decomposes at low temperatures forming free radical initiators with short half lives, therein reducing the molding temperature of the high vicat layer and subsequently reducing the temperature and/or time the softer thermoplastic layer is exposed to the high heat.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 12/118,860, filed May 12, 2008, the disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention is directed to a golf ball having a thermoset layer molded over a thermoplastic layer. More specifically, a thermoset layer that comprises a low temperature peroxide which releases free radical initiators having short half lives to either reduce the molding temperature or the time of molding.

BACKGROUND OF THE INVENTION

Early solid golf balls were generally two piece balls, i.e., comprising a core and a cover. More recently developed solid balls are comprised of a core, a core layer or mantle layer, and a cover, in order to improve the playing characteristics of the ball.

The prior art is comprised of a variety of golf balls that have been designed to provide particular playing characteristics. These characteristics are generally the initial velocity and spin of the golf ball, which can be optimized for various types of players. For instance, certain players prefer a ball that has a high spin rate in order to control and stop the golf ball. Other players prefer a ball that has a low spin rate and high resiliency to maximize distance. Generally, a golf ball having a hard core and a soft cover will have a high spin rate. Conversely, a golf ball having a hard cover and a soft core will have a low spin rate. Golf balls having a hard core and a hard cover generally have very high resiliency for distance, but are hard feeling and difficult to control around the greens. Various prior art references have been directed to adding a mantle layer or second cover layer to improve the playability of solid golf balls.

The spin rate of golf balls is the end result of many variables, one of which is the distribution of the density or specific gravity within the ball. Spin rate is an important characteristic of golf balls for both skilled and recreational golfers. High spin rate allows the more skilled players, such as PGA professionals and low handicapped players, to maximize control of the golf ball. A high spin rate golf ball is advantageous for an approach shot to the green. The ability to produce and control backspin to stop the ball on the green and side spin to draw or fade the ball substantially improves the player's control over the ball. Hence, the more skilled players generally prefer a golf ball that exhibits high spin rate.

On the other hand, recreational players who cannot intentionally control the spin of the ball generally do not prefer a high spin rate golf ball. For these players, slicing and hooking are the more immediate obstacles. When a club head strikes a ball, an unintentional side spin is often imparted to the ball, which sends the ball off its intended course. The side spin reduces the player's control over the ball, as well as the distance the ball will travel. A golf ball that spins less tends not to drift off-line erratically if the shot is not hit squarely on the club face. The low spin ball will not cure the hook or the slice, but the lower spin will reduce the adverse effects of the side spin. Hence, recreational players prefer a golf ball that exhibits low spin rate.

There is a significant need in the industry for a ball having a large diameter but low compression core and surrounded by a harder outer core layer, i.e. a relatively large thermoplastic core with a thermoset core layer about it. As used herein, the term “thermoset” material refers to an irreversible, solid polymer that is the product of the reaction of two or more prepolymer precursor materials. However, traditionally there have been significant manufacturing difficulties when trying to compression mold a thermoset polybutadiene-comprising layer over a thermoplastic core layer. Typical results include the melting, distortion and flow of the thermoplastic core into the surrounding rubber layer. These problems can be increased due to the temperature, time and pressure required to thoroughly cure the rubber. The temperatures required usually range between 157° C. and 177° C. which can be significantly higher than the melting temperature of the underlying thermo-plastic layer. Additionally, the exotherm generated from the curing reaction of a 11-15 minute cure can elevate the rubber temperature even higher. Thus, there remains a need to minimize the temperature and/or the time that the thermoplastic material is exposed. Ball construction materials are necessary that teach the lowering of molding temperature in which a thermoplastic material is exposed to, or that teach shortening of the exposure time. Such construction will allow the compression molding of a thermoset layer over a thermoplastic layer without significant flow of the thermoplastic layer into the thermoset layer.

Other prior art golf balls have multiple core layers to provide desired playing characteristics. For example, U.S. Pat. No. 6,815,480 discloses blends of highly neutralized polymers (HNP) with Hytrel® and other high melt temperature materials but not discrete layers of high melt materials.

U.S. Pat. Nos. 6,057,403, 6,213,895, and 6,585,608, issued to Sullivan, disclose thermoplastic core layers but do not disclose highly neutralized polymers or the use of a heat resistant outer core layer such as disclosed in this invention.

U.S. Pat. No. 6,450,901 discloses outer covers comprising blends of very low modulus ionomers (VLMI) with a high melt ionomer (Surlyn 8549, vcat of 84° C.) having a vicat softening temp of 74° C. or more, and preferably 84° C. or more. However, no disclosure of a discrete layer of the high vicat material or of HNPs is made.

These and other objects and features of the invention will be apparent from the following summary and description of the invention, the drawings and from the claims.

SUMMARY OF THE INVENTION

The invention provides for a golf ball that having an inner core that comprises a partially or fully neutralized ionomer and has a first vicat softening point temperature of less than 75° C., the inner core having a surface hardness of less than 85 Shore C and a compression of less than 80. Encasing the inner core is a heat resistant thermoset layer having a second vicat softening point temperature of at least 20° C. greater than the first, preferably 50° C. greater, and more preferably 100° C. greater. The heat resistant layer comprising a peroxide that decomposes at low temperatures forming free radical initiators with short half lives, wherein the free radical initiators with short half lives cause the molding temperature and time of the heat resistant layer to be reduced, therein restricting flow of the thermoplastic inner core into the thermoset layer. A cover layer is formed about the heat resistant layer cover layer to complete the golf ball.

An embodiment of the golf ball provides for heat resistant layer comprising of peroxides having a half life of under ten minutes at a temperature of 133° C. These peroxides can include low temperature peroxides such as 1,1-di(t-butylperoxy)cyclo-hexane, 1,1-di(t-butyperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-amylperoxy)cyclo-hexane, or t-butyl peroxy-(cis-3-carboxy)propenoate and these peroxides may be blended with compositions that comprise compositions such as polyetheramides; polyetheresters; polyesteramides; thermoplastic urethanes; polyesters such as polybutylene terephthalate or polyethylene terephthalate or copolymers thereof; polycarbonates; polyamides; polypropylene; polyethylene; or mixtures thereof. The inner core of the ball further comprises dynamically vulcanized thermoplastic elastomers; suitable functionalized styrene-butadiene elastomers; thermoplastic polyetheresters; polyetheramides; thermoplastic polyesters; or mixtures thereof.

Another embodiment of the invention includes an intermediate layer about the inner core and the heat resistant layer is formed between it and the cover.

An object of the invention is to provide a method of compression molding polybutadiene/ZDA/peroxide base over thermoplastic centers without the introduction of melting, distortion, or flow of the thermoplastic center into the surrounding rubber layer. This can be achieved by the use of free radical initiators having short half lives at low temperatures to compression mold a thermoset layer over a thermoplastic layer without significant flow of the thermoplastic layer into the thermoset layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a golf ball formed according to the present invention having a partly or highly neutralized ionomer inner core, an outer core layer using free radiator initiators with short half lives at low temperatures molded over the center, and a polymer cover layer.

FIG. 2 is a cross-sectioned view of a four piece golf ball comprising: a thermoset polybutadiene inner core; a partly or highly neutralized ionomer intermediate core layer having a low vicat softening point temperature; an outer core layer using free radical initiators with short half lives at low temperatures; and a cover layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a multi-piece golf ball comprising two or more core layers in which at least one layer is a low melting point thermoplastic material and an adjacent outer core layer is a high melting point thermoset material, preferably a heat resistant layer. This combination facilitates compression molding of a thermosetting polybutadiene comprising layer over the thermoplastic layers and the present invention successfully performs this construction without the thermoplastic material bleeding into the thermoset material.

The thermoset material is typically formed from a castable reactive liquid material. The preferred materials for this layer include, but are not limited to thermoset urethanes and polyurethanes, thermoset urethane ionomers and thermoset urethane epoxies. Examples of suitable polyurethane ionomers are disclosed in U.S. Pat. No. 5,692,974, filed Jun. 7, 1995, the disclosure of which is hereby incorporated by reference in its entirety in the present application. Conventionally, thermoset polyurethanes are prepared using a diisocyanate, such as 2,4-toluene diisocyanate (TDI) or methylenebis-(4-cyclohexyl isocyanate) (HMDI) and a polyol which is cured with a polyamine, such as methylenedianiline (MDA), or a a trifunctional glycol, such as N,N,N,N-tetrakis(2-hydroxpropyl)ethylendiamine. However, the present invention is not limited to just these specific types of thermoset polyurethanes.

The invention provides constructions and methods of molding that allow for a cross-linked polybutadiene composition (normally the inner core formulations) as an outermost core or inner cover layer molded over high resilience thermoplastic core materials such as highly neutralized ionomers. The use of high melting point or high vicat softening point material provides for easier over-molding of a thermo-plastic composition (such as a polybutadiene core formulation) and minimizes the “leakage” of inner core material out of the mold equator as the outer core layer cures.

For the purposes of this invention, high vicat is defined as at least 80° C., preferably at least 90° C., and most preferably at least 100° C. and includes straight materials as well as blends of two or more materials, said blend having a vicat of at least 80° C. Included herein are blends of a low vicat and a high vicat, as long as the blend composition has a vicat of over 80° C. For example, a high vicat could include a blend of an highly neutralized polymer (HNP) such as a HNP 2000 (vicat of 54° C.) and a Hytrel®4069 (vicat of 134° C.). Another example of a high vicat material is Surlyn SG201U, which is a Surlyn/polyester alloy having a vicat of 190° C. Such ionomer resins and the manner in which they are made is well known in the art as described in U.S. Pat. No 3,262,272. Such ionomer resins are commercially available from DuPont Co. under the tradename SURLYN® and from Exxon under the tradename Iotek®. Some particularly suitable SURLYNS® include SURLYN® 8549, SURLYN® 8610, SURLYN® 8940, SURLYN® 8527, and SURLYN® 8660. A suitable ionomer from Exxon include IOTEK® 8000.

PHYSICAL PROPERTY COMPARISON Physical Surlyn Surlyn lotek Surlyn Surlyn Surlyn Property 8549 8610 8000 8940 8527 8660 Melt Index 2.3 1.3 0.8 2.8 1 10 (g/10 min) Melt temperature 100 86 83 94 93 95 (° C.) Vicat softening 84 57 54 63 73 71 (° C.) Tensile strength 32 34 33 33 29 23.4 (MPa) Elongation (%) 300 420 370 470 450 470 Flex modulus 390 290 320 350 220 230 (MPa) Haze (%) 4 5 5 5 6 11 Shore D 61 58 60 65 0 62

PHYSICAL PROPERTY COMPARISON FOR HYTREL ® Grades Hytrel ® Hytrel ® Hytrel ® Hytrel ® Hytrel ® Physical Property 3078 4069 5556 6356 7246 Melt Index 5.0 8.5 7.5 8.5 12.5 (g/10 min) @190 C. @220° C. @220° C. @230° C. @240° C. Melt temperature (° C.) 170 193 203 211 218 Vicat softening (° C.) 83 134 180 195 207 Tensile strength 26.2 27.6 40 41 45.8 (Mpa) Elongation (%) 700 600 500 420 360 Flex. Modulus (Mpa) 28 55 207 330 570 Hardness 30 40 55 63 72 (Shore D)

PHYSICAL PROPERTY COMPARISON FOR Pebax ® Grades Physical Pebax ® Pebax ® Pebax ® Pebax ® Pebax ® Pebax ® Property 2533 3533 4033 5533 6333 7033 Melt Volume 14.0 12.0 9.0 8.0 8.0 6.0 flow rate (cm3/10 min) at 235 C. (ISO 1133) Melt 148 152 168 168 172 174 temperature (° C.) Vicat 60 74 132 144 161 165 softening (° C.) Tensile strength 34.1 38.6 39.3 50.3 55.9 57.2 (Mpa) Flex. Modulus 15 19.3 90 200 338 462 (Mpa) Hardness 25 35 40 55 63 69 (Shore D) Pebax ® is a block copolymer of polyether-amide from Arkema.

PHYSICAL PROPERTY COMPARISON FOR Estane ® Grades Physical Estane ® Estane ® Estane ® Estane ® Estane ® Estane ® Property 58280 58810 58092 58130 58137 58091 Melt NA NA NA 220 228 223 temperature (° C.) Tensile 24.9 37.9 31.7 38.6 37.2 29.0 strength (Mpa) Elongation 750 525 450 530 430 160 (%) Flexural 16.2 37.7 NA NA NA NA modulus (Mpa) Vicat 66 110 NA NA NA NA Softening (° C.) Hardness 27 42 45 50 67 70 (Shore D) Estane ® is a thermoplastic urethane either ether or ester urethane type from Lubrizol Inc.

PHYSICAL PROPERTY COMPARISON Rilsan ® Rilsan ® Xylex ® Xylex ® Physical Property AMNO BMNO Xylex ® X7110 X7300 X8300 Melt Flow Index NA NA 9.0 21 15 (g/10 min) at 265 C. Melt temperature 174 189 NA NA NA (° C.) Vicat softening(° C.) NA NA 106 108 96 Tensile strength 65.5 68.9 48.3 52.0 46 (Mpa) Elongation (%) 400 390 150 150 150 Flex. Modulus 1100 1100 1750 2000 1680 (Mpa) Hardness (Rockwell- 106 108 NA NA NA R scale) Rilsan ® AMNO is Polyamide 12 from Arkema; Rilsan ® BMNO Polyamide 11 from Arkema. Xylex ® is polycarbonate/polyester blend from Sabic Innovative Plastics

Highly neutralized ionomers (HNP), such as HPF 1000 and HPF 2000 (both manufactured by DuPont), have vicats of 59° C. and 54° C. respectively. While the HPFs have very PBR-like properties of high coefficient of restitution (COR) and relatively soft compressions as molded spheres (versus other Surlyn grades) which makes them good candidates for core materials, however, their low melting points make them difficult to compression mold over when using a preferred polybutadiene composition. The present invention teaches a successful method for making a ball having an HNP inner core surrounded by a compression molded polybutadiene composition. Typically, during the compression molding of this type of outer core, the inner core melts and has a tendency to flow out at the mold equator, giving a core that has poor durability and inconsistent properties. The present invention has solved this problem by covalently cross-linking the thermoset layer with a free radical initiator (peroxide) having short half lives at low temperatures therein allowing the compression mold of a thermoset layer over a thermoplastic layer without a significant flow of the plastic layer into the thermoset layer. A high melt thermoplastic is preferably injection molded around the HNP inner core. By using free radical initiator peroxide and thus forming the layer at a relatively lower temperature, the HNP inner core is not exposed to enough temperature or if the temperature is not a significant factor then the shorter mold time will prevent the melt of the HNP and therein reduce the flow of the HNP.

Preferred high melt thermoplastics materials are polyetheramides (Pebax®, which is available from Elf-Atochem), and polyetheresters which include materials which are commercially available from DuPont under the tradename Hytrel®, polyesteramides, thermoplastic urethanes, polyesters such as polybutylene terephthalate (PBT) or polyethylene terephthalate (PET) or copolymers thereof, polycarbonates, polyamides, polypropylene, polyethylene, thermoplastic vulcanizates (TPVs) and any disclosed in such U.S. Pat. Nos. 6,762,244, 6,284,840 and 6,302,808, the disclosures of which are hereby incorporated by reference in their entirety in the present application. The vicat softening temperature for high density polyethylene (HDPE) is about 128° C.; for polypropylene 153° C., Nylon 66 about 261° C., a Surlyn/polyester alloy sold by DuPont as Surlyn Supergloss G201U has a vicat of 190° C. Hytrel® grades have a range of about 83-207° C. and Pebax® resins have a range of 74 to 165° C. Blends or alloys of any of these materials with any low melt materials such as Surlyn or HNPs may also be employed. Vicat temperature is measured per ASTM D1525.

The melting and flow of thermoplastic layers in these types of constructions is primarily due to the temperature, time and pressure required to thoroughly cure the rubber. The temperatures that are typically used range between 147° C.-177° C. which can be significantly higher than the melting temperature of the underlying thermo-plastic layer. Additionally, the exothermic heat generated from the peroxide decomposition and curing reaction can elevate the rubber temperature even higher. The typical 11-15 minute cure time is also an important factor. To overcome this manufacturing problem, the present invention employs peroxides that will significantly decompose at lower temperatures. Typically, these are low temperature peroxides that generate free radicals having half lives of less than ten minutes at temperatures of about 133° C. or less. These include low temperature peroxides such as 1,1-di(t-butylperoxy)cyclo-hexane, 1,1-di(t-butyperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-amylperoxy)cyclo-hexane, or t-butyl peroxy-(cis-3-carboxy)propenoate and these peroxides may be blended with compositions that comprise compositions such as polyetheramides; polyetheresters; polyesteramides; thermoplastic urethanes; polyesters such as polybutylene terephthalate or polyethylene terephthalate or copolymers thereof; polycarbonates; polyamides; polypropylene; polyethylene; or mixtures thereof. The inner core of the ball further comprises dynamically vulcanized thermoplastic elastomers; suitable functionalized styrene-butadiene elastomers; thermoplastic polyetheresters; polyetheramides; thermoplastic polyesters; or mixtures thereof.

Another embodiment of the invention includes an intermediate layer about the inner core and the heat resistant layer is formed between it and the cover.

The low temperature decomposition peroxide can also be used in conjunction with a higher temperature composition peroxide alone with step-wise multiple temperature cure profiles or ramped temperature cure profiles to achieve the desired level of cure. Once the core is made, any number or types of covers can be put over the core to produce a golf ball of the present invention. The thermoplastic center materials include but are not limited to HNPs, Surlyn, and Fusabond. The thermoset materials include but are not limited to polybutadiene, polyisoprene and silicone rubber.

When golf balls are prepared according to the invention, they typically will have dimple coverage greater than about 60 percent, preferably greater than about 65 percent, and more preferably greater than about 75 percent. The flexural modulus of the cover material used on the golf balls, as measured by ASTM method D6272 98, Procedure B, is typically greater than about 10 kpsi, and is preferably from about 10 kpsi to 150 kpsi, more preferably 15 to 70 kpsi. As discussed herein, the outer cover layer is preferably formed from a relatively soft ionomer, poly-urethane, or polyurea material. In particular, the material of the outer cover layer should have a material hardness, as measured by ASTM-D2240, less than about 70 Shore D, more preferably between about 25 and about 50 Shore D, and most preferably between about 40 and about 48 Shore D. An intermediate core layer preferably has a material hardness of less than about 70 Shore D, more preferably less than 65 Shore D, and most preferably, between about 25 and 65 Shore D.

The overall outer diameter (“OD”) of the thermoplastic inner core is less than about 1.650 inches, preferably, no greater than 1.620 inches, more preferably between about 1.000 and about 1.510 inches, and most preferably less than 1.50 inches. The outside diameter of the intermediate core layer is preferably between 1.580 inches and about 1.650 inches, more preferably between about 1.590 inches to about 1.630 inches, and most preferably between about 1.600 inches to about 1.630 inches.

The core of the golf ball may also be extremely large in relation to the rest of the ball. For example, in one embodiment, the core makes up about 90 percent to about 98 percent of the ball, preferably about 94 percent to about 96 percent of the ball. In this embodiment, the diameter of the core is preferably about 1.54 inches or greater, preferably about 1.55 inches or greater. In one embodiment, the core diameter is about 1.59 inches or greater. In another embodiment, the diameter of the core is about 1.64 inches or less.

The cover layer typically has a thickness to provide sufficient strength, good performance characteristics, and durability. The thickness of the cover layer may be from about 0.005 inches to about 0.100 inches, preferably about 0.007 inches to about 0.035 inches. In one embodiment, the cover layer thickness is from about 0.02 inches to about 0.35 inches. In another embodiment, the cover preferably has a thickness of about 0.02 inches to about 0.12 inches, preferably about 0.1 inches or less, more preferably about 0.07 inches or less. In yet another embodiment, the outer cover has a thickness from about 0.02 inches to about 0.07 inches. In still another embodiment, the cover thickness is about 0.05 inches or less, preferably from about 0.02 inches to about 0.05 inches. For example, the cover layer may be between about 0.02 inches and about 0.045 inches, preferably about 0.025 inches to about 0.04 inches thick. In one embodiment, the outer cover layer is about 0.03 inches thick.

The range of thicknesses for an intermediate layer of a golf ball is large because of the vast possibilities when using an intermediate layer, i.e., as an outer core layer, an inner cover layer, a wound layer, a moisture/vapor barrier layer. When used in a golf ball of the invention, the intermediate layer, or inner cover layer, may have a thickness about 0.3 inches or less. In one embodiment, the thickness of the intermediate layer is from about 0.002 inches to about 0.1 inches, preferably about 0.01 inches or greater. In one embodiment, the thickness of the intermediate layer is about 0.09 inches or less, preferably about 0.06 inches or less. In another embodiment, the intermediate layer thickness is about 0.05 inches or less, more preferably about 0.01 inches to about 0.045 inches. In one embodiment, the thickness of the intermediate layer is about 0.02 inches to about 0.04 inches. In another embodiment, the intermediate layer thickness is from about 0.025 inches to about 0.035 inches. In yet another embodiment, the thickness of the shield layer is about 0.035 inches. In still another embodiment, the inner cover layer is from about 0.03 inch to about 0.035 inch thick. Varying combinations of these ranges of thickness for the shield and outer cover layers may be used in combination with other embodiments described herein.

The ratio of the thickness of the intermediate layer to the outer cover layer is preferably about 10 or less, preferably from about 3 or less. In another embodiment, the ratio of the thickness of the intermediate layer to the outer cover layer is about 1 or less.

Accordingly, it is preferable that the golf balls of the present invention have a intermediate layer with a flexural modulus of about 500 psi to about 500,000 psi according to ASTM D-6272-98. More preferably, the flexural modulus of the intermediate layer is about 1,000 psi to about 250,000 psi. Most preferably, the flexural modulus of the intermediate layer is about 2,000 psi to about 200,000 psi. The flexural modulus of the cover layer is preferably about 2,000 psi or greater, and more preferably about 5,000 psi or greater. In one embodiment, the flexural modulus of the cover is from about 10,000 psi to about 150,000 psi. More preferably, the flexural modulus of the cover layer is about 15,000 psi to about 120,000 psi. Most preferably, the flexural modulus of the cover layer is about 18,000 psi to about 110,000 psi. In another embodiment, the flexural modulus of the cover layer is about 100,000 psi or less, preferably about 80,000 or less, and more preferably about 70,000 psi or less. For example, the flexural modulus of the cover layer may be from about 10,000 psi to about 70,000 psi, from about 12,000 psi to about 60,000 psi, or from about 14,000 psi to about 50,000 psi.

In one embodiment, when the cover layer has a hardness of about 50 Shore D to about 67 Shore D, the cover layer preferably has a flexural modulus of about 55,000 psi to about 70,000 psi.

In one embodiment, the ratio of the flexural modulus of the intermediate layer to the cover layer is about 0.003 to about 50. In another embodiment, the ratio of the flexural modulus of the intermediate layer to the cover layer is about 0.006 to about 4.5. In yet another embodiment, the ratio of the flexural modulus of the intermediate layer to the cover layer is about 0.11 to about 4.5.

In one embodiment, the compositions of the invention are used in a golf ball with multiple cover layers having essentially the same hardness, but differences in flexural moduli. In this aspect of the invention, the difference between the flexural moduli of the two cover layers is preferably about 5,000 psi or less. In another embodiment, the difference in flexural moduli is about 500 psi or greater. In yet another embodiment, the difference in the flexural moduli between the two cover layers, wherein at least one is reinforced is about 500 psi to about 10,000 psi, preferably from about 500 psi to about 5,000 psi. In one embodiment, the difference in flexural moduli between the two cover layers formed of unreinforced or unmodified materials is about 1,000 psi to about 2,500 psi.

The specific gravity of a cover or intermediate layer is preferably at least about 0.7. In one embodiment, the specific gravity of the intermediate layer or cover is about 0.8 or greater, preferably about 0.9 or greater. For example, in one embodiment, the golf ball has an intermediate layer with a specific gravity of about 0.9 or greater and a cover having a specific gravity of about 0.95 or greater. In another embodiment, the intermediate layer or cover has a specific gravity of about 1.00 or greater. In yet another embodiment, the specific gravity of the intermediate layer or cover is about 1.05 or greater, preferably about 1.10 or greater. In still another embodiment, the specific gravity of the intermediate layer or cover is about 1.0 to about 1.3.

The core may have a specific gravity of about 1.00 or greater, preferably 1.05 or greater. For example, a golf ball of the invention may have a core with a specific gravity of about 1.10 or greater and a cover with a specific gravity of about 0.95 or greater.

Although the United States Golf Association (“USGA”) specifications limit the minimum size of a competition golf ball to 1.680 inches. There is no specification as to the maximum diameter. Golf balls of any size, however, can be used for recreational play. The preferred diameter of the present golf balls is from about 1.680 inches to about 1.800 inches. The more preferred diameter is from about 1.680 inches to about 1.760 inches. The most preferred diameter is about 1.680 inches to about 1.740 inches.

It should be understood, especially to one of ordinary skill in the art, that there is a fundamental difference between “material hardness” and “hardness, as measured directly on a golf ball.” Material hardness is defined by the procedure set forth in ASTM-D2240 and generally involves measuring the hardness of a flat “slab” or “button” formed of the material of which the hardness is to be measured. Hardness, when measured directly on a golf ball (or other spherical surface) is a completely different measurement and, therefore, results in a different hardness value. This difference results from a number of factors including, but not limited to, ball construction (i.e., core type, number of core and/or cover layers, etc.), ball (or sphere) diameter, and the material composition of adjacent layers. It should also be understood that the two measurement techniques are not linearly related and, therefore, one hardness value cannot easily be correlated to the other.

As used herein, the term “about,” used in connection with one or more numbers or numerical ranges, should be understood to refer to all such numbers, including all numbers in a range.

The overall outer diameter (OD) of the core (including the center and any intermediate layers, the outer core layer or windings) together with the inner cover layer of the golf balls of the present invention is about 1.58 inches to about 1.64 inches, preferably about 1.60 inches to about 1.63 inches, more preferably about 1.62 inches to about 1.63 inches and most preferably about 1.62 inches. The outer diameter of the center of the core is about 1.00 inches to about 1.60 inches. In another embodiment, the outer diameter of the core (including the center and any intermediate mantle layer(s) or windings) without the inner cover layer is about 1.5 inches to about 1.6 inches, preferably about 1.55 inches to about 1.58 inches.

The present multilayer golf ball can have an overall diameter of any size. Although the United States Golf Association (USGA) specifications limit the minimum size of a competition golf ball to more than 1.680 inches in diameter, there is no specification as to the maximum diameter. Moreover, golf balls of any size can be used for recreational play. The preferred diameter of the present golf balls is from about 1.680 inches to about 1.800 inches. The more preferred diameter is from about 1.680 inches to about 1.760 inches. The most preferred diameter is about 1.680 inches to about 1.740 inches.

The cores and inner cover of the golf balls of the present invention can be made by any conventional process employed in the golf ball art. For example, the solid centers can be either injection or compression molded. Similarly, the wound centers employed in the present invention can be produced through conventional means. The inner cover layer and any mantle or outer core layer(s) are subsequently injection or compression molded about the core. However, due to the very thin thickness (less than 0.05″), it is not practical to form the cover layers of the ball using conventional injection or compression molding techniques ordinarily employed in the golf ball art for applying cover materials. These conventional ball molding processes are not capable of easily applying such thin outer cover layers over a solid spherical surface. Accordingly, it has been found that the use of a castable, reactive material which is applied in a fluid form makes it possible to obtain very thin outer cover layers on golf balls. Specifically, it has been found that castable, reactive liquids which react to form a thermoset material provide desirable very thin outer cover layers.

The castable, reactive liquid employed to form the thermoset material can be applied over the inner core using a variety of application techniques such as spraying, dipping, spin coating or flow coating methods which are well known in the art. An example of a suitable coating technique is that which is disclosed in U.S. Pat. No. 5,733,428, filed May 2, 1995 entitled “Method And Apparatus For Forming Polyurethane Cover On A Golf Ball”, the disclosure of which is hereby incorporated by reference in its entirety in the present application. Similarly, U.S. Pat. No. 5,006,297 to Brown et al. and U.S. Pat. No. 5,334,673 to Wu both disclose suitable coating techniques which may be utilized to apply the castable reactive liquids employed in the present invention. The disclosures of these patents are hereby incorporated by reference in their entirety. However, the method of the invention is not limited to the use of these techniques.

EXAMPLES

The following examples are provided only for the purpose of illustrating the invention and are not to be construed as limiting the invention in any manner.

Prophetic Example 1

As shown in FIG. 1, a golf ball 10 comprises a thermoplastic inner core 11 formed from HNP 2000 material (DuPont) which has a low vicat and a low melting point of less than 100° C., and a Shore C surface hardness of less than 85, and a compression of less than 80. The ball comprises a thermoset heat resistant core layer 12 comprising a peroxide, such as 1,1-di(t-butylperoxy)cyclohexane that decomposes at low temperatures forming free radical initiators with short half lives of less than ten minutes at 133° C., therein reducing the temperature and/or time required by the core layer 12 to mold over the thermoplastic inner core 11; and, a cast ionomer, polyurethane or polyurea cover 13. The inner core 11 has a diameter of about 1.00 to 1.56 inches, while the heat resistant core layer 12 has a thickness of about 0.03 to 0.28 inches, and the cover 13 has a thickness of about 0.03 to 0.06 inch.

Prophetic Example 2

Another embodiment of the invention is depicted in FIG. 2. A ball 20 includes an inner core 22 comprising of a thermoset polybutadiene composition and having a vicat of about 75° or less. Encasing the inner core 22 is a thermoplastic core layer 24 comprising a partially or fully neutralized ionomer having a low vicat softening point temperature. Disposed around the core layer 24 is a thermoset heat resistant layer 26 comprising a peroxide such as 1,1-di(t-amylperoxy)cyclohexane that decomposes at low temperatures forming free radical initiators with a short half lives of under 10 minutes at 270° F., therein reducing the temperature required by the core layer 26 to mold over the thermoplastic inner core 24. Completing the ball 20 is a cover layer 28 comprising ionomer, polyurethane, or polyurea material.

The heat resistant layers can be made of thermoplastic elastomers including dynamically vulcanized thermoplastic elastomers and blends thereof. Suitable dynamically vulcanized thermoplastic elastomers include Santoprene®., Sarlink®, Vyram®, Dytron® and Vistaflex®. Santoprene® is the trademark for a dynamically vulcanized PP/EPDM. Santoprene® 203-40 is an example of a preferred Santoprene® and is commercially available from Advanced Elastomer Systems.

Examples of suitable functionalized styrene-butadiene elastomers include Kraton FG-1901x and FG-1921x, available from the Shell Corporation. Examples of suitable thermoplastic polyurethanes include Estane® 58133, Estane® 58134 and Estane® 58144, which are available from the B.F. Goodrich Company. Further, the materials may be in the form of a foamed polymeric material. For example, suitable metallocene polymers include foams of thermoplastic elastomers based on metallocene single-site catalyst-based foams. Such metallocene-based foams are commercially available from Sentinel Products of Hyannis, Mass.

Suitable thermoplastic polyetheresters include Hytrel® 3078, Hytrel® G3548W, and Hytrel® G4078W which are commercially available from DuPont. Suitable thermoplastic polyetheramides include Pebax® 2533, Pebax® 3533, Pebax® 1205 and Pebax® 4033 which are available from Elf-Atochem. Suitable thermoplastic polyesters include polybutylene terephthalate.

Suitable thermoplastic ionomer resins are obtained by providing a cross metallic bond to polymers of mono-olefin with at least one member selected from the group consisting of unsaturated mono- or di-carboxylic acids having 3 to 12 carbon atoms and esters thereof. The polymer contains 1 to 50% by weight of the unsaturated mono- or di-carboxylic acid and/or ester thereof. More particularly,low modulus ionomers, such as acid-containing ethylene copolymer ionomers, include E/X/Y copolymers where E is ethylene, X is a softening comonomer such as acrylate or methacrylate present in 0-50 (preferably 0-25, most preferably 0-2), weight percent of the polymer, and Y is acrylic or methacrylic acid present in 5-35 (preferably 10-35, most preferably 15-35, making the ionomer a high acid ionomer) weight percent of the polymer, wherein the acid moiety is neutralized 1-100% (preferably at least 40%, most preferably at least about 60%) to form an ionomer by a cation such as lithium*, sodium*, potassium, magnesium*, calcium, barium, lead, tin, zinc* or aluminum (*=preferred), or a combination of such cations. Specific acid-containing ethylene copolymers include ethylene/acrylic acid, ethylene/methacrylic acid, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl methacrylate, and ethylene/ acrylic acid/n-butyl methacrylate. Preferred acid-containing ethylene copolymers include ethylene/methacrylic acid, ethylene/acrylic acid, ethylene/methacrylic acid/n-butyl acrylate, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methyl acrylate and ethylene/acrylic acid/methyl acrylate copolymers. The most preferred acid-containing ethylene copolymers are ethylene/methacrylic acid, ethylene/acrylic acid, ethylene/(meth)acrylic acid/n-butyl acrylate, ethylene/(meth)acrylic acid/ethyl acrylate, and ethylene/(meth)acrylic acid/methyl acrylate copolymers.

Thermoplastic blends comprise about 1% to about 99% by weight of a first thermoplastic and about 99% to about 1% by weight of a second thermoplastic. Preferably the thermoplastic blend comprises about 5% to about 95% by weight of a first thermoplastic and about 5% to about 95% by weight of a second thermoplastic. In a preferred embodiment of the present invention, the first thermoplastic material of the blend is a dynamically vulcanized thermoplastic elastomer, such as Santoprene®.

Fillers typically include materials such as tungsten, zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, metals, metal oxides and salts, regrind (recycled core material typically ground to about 30 mesh particle), high-Mooney-viscosity rubber regrind, and the like. Fillers may be added to one or more portions of the golf ball and typically may include processing aids or compounds to affect Theological and mixing properties, density-modifying fillers, fillers to improve tear strength, or reinforcement fillers, and the like. The fillers are generally inorganic, and suitable fillers include numerous metals or metal oxides, such as zinc oxide and tin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay, tungsten, tungsten carbide, an array of silicas, and mixtures thereof. Fillers may also include various foaming agents or blowing agents which may be readily selected by one of ordinary skill in the art. Fillers may include polymeric, ceramic, metal, and glass microspheres may be solid or hollow, and filled or unfilled. Fillers are typically also added to one or more portions of the golf ball to modify the density thereof to conform to uniform golf ball standards. Fillers may also be used to modify the weight of the center or at least one additional layer for specialty balls, e.g., a lower weight ball is preferred for a player having a low swing speed.

The invention also includes, if desired, a method to convert the cis-isomer of the polybutadiene resilient polymer component to the trans-isomer during a molding cycle and to form a golf ball. A variety of methods and materials suitable for cis-to-trans conversion have been disclosed in U.S. Pat. No. 6,162,135 and U.S. application Ser. No. 09/461,736, filed Dec. 16, 1999; Ser. No. 09/458,676, filed Dec. 10, 1999; and Ser. No. 09/461,421, filed Dec. 16, 1999, each of which are incorporated herein, in their entirety, by reference.

The materials used in forming either the golf ball center or any portion of the core, in accordance with the invention, may be combined to form a mixture by any type of mixing known to one of ordinary skill in the art. Suitable types of mixing include single pass and multi-pass mixing. Suitable mixing equipment is well known to those of ordinary skill in the art, and such equipment may include a Banbury mixer, a two-roll mill, or a twin screw extruder.

Conventional mixing speeds for combining polymers are typically used. The mixing temperature depends upon the type of polymer components, and more importantly, on the type of free-radical initiator. Suitable mixing speeds and temperatures are well-known to those of ordinary skill in the art, or may be readily determined without undue experimentation.

The mixture can be subjected to, e.g., a compression or injection molding process, to obtain solid spheres for the center or hemispherical shells for forming an intermediate layer. The temperature and duration of the molding cycle are selected based upon reactivity of the mixture. The molding cycle may have a single step of molding the mixture at a one particular temperature for a fixed duration. The molding cycle may also include a two-step process, in which the polymer mixture is held in the mold at an initial temperature for an initial duration of time, followed by holding at a second, typically higher temperature for a second duration of time. In a preferred embodiment of the current invention, a single-step cure cycle is employed. The materials used in forming either the golf ball center or any portion of the core, in accordance with the invention, may be combined to form a golf ball by an injection molding process, which is also well-known to one of ordinary skill in the art. Although the curing time depends on the various materials selected, those of ordinary skill in the art will be readily able to adjust the curing time upward or downward based on the particular materials used and the discussion herein.

The properties such as hardness, Bayshore resilience modulus, center diameter and layer thickness of the golf balls of the present invention have been found to affect play characteristics such as spin, initial velocity and feel of golf balls.

The golf ball of the present invention can have an overall diameter of any size. Although the United States Golf Association (USGA) specifications limit the minimum size of a competition golf ball to more than 1.680 inches in diameter, there is no specification as to the maximum diameter. Moreover, golf balls of any size can be used for recreational play. The preferred diameter of the present golf balls is from about 1.680 inches to about 1.800 inches. The more preferred diameter is from about 1.680 inches to about 1.760 inches. The most preferred diameter is about 1.680 inches to about 1.740 inches.

While it is apparent that the illustrative embodiments of the invention herein disclosed fulfill the objectives stated above, it will be appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments which come within the spirit and scope of the present invention. 

1. A golf ball comprising: a thermoplastic inner core comprising a partially or fully neutralized ionomer having a first vicat softening point temperature, the inner core having a surface hardness of less than 85 Shore C and a compression of less than 80; a heat resistant thermoset layer encasing the inner core, the thermoset layer having a second vicat softening point temperature of at least 20° C. greater than the first; and comprising a peroxide that decomposes at low temperatures forming free radical initiators with short half lives; and a cover layer, wherein the free radical initiators have short half lives causing the molding temperature and time of the heat resistant layer to be reduced, therein restricting flow of the thermoplastic inner core into the thermoset layer.
 2. The golf ball according to claim 1, wherein the first vicat softening point temperature is 75° C. or less.
 3. The golf ball according to claim 2, wherein the second vicat softening ppint temperature is at least 50° C. greater than the first.
 4. The golf ball according to claim 2, wherein the second vicat softening ppint temperature is at least 100° C. greater than the first.
 5. The golf all according to claim 1, wherein the peroxide is 1,1-di(t-butylperoxy)cyclohexane, or 1,1-di(t-butylperoxy) -3,3,5-trimethylcyclohexane, or 1,1-di(t-amylperoxy)cyclohexane or tbutyl peroxy-(cis-3-carboxy)propenoate.
 6. The golf ball according to claim 5, wherein the peroxide has a half life of less than 10 minutes at 133° C.
 7. The golf ball according to claim 1, wherein the thermoplastic inner core has a diameter of about 1.00 inch or less.
 8. The golf ball according to claim 1, wherein the heat resistant thermoset layer comprises polyetheramides; polyetheresters; polyesteramides; thermoplastic urethanes; polyesters such as polybutylene terephthalate or polyethylene terephthalate or copolymers thereof; polycarbonates; polyamides; polypropylene; polyethylene; or mixtures thereof.
 9. The golf ball according to claim 1, wherein the thermoplastic inner core further comprises of dynamically vulcanized thermoplastic elastomers; suitable functionalized styrene-butadiene elastomers; thermoplastic polyetheresters; polyetheramides; thermoplastic polyesters; or mixtures thereof.
 10. The golf ball according to claim 1, wherein the heat resistant thermoset layer has a thickness of 0.050 inch or less.
 11. The golf ball according to claim 1, wherein the heat resistant thermoset layer has a thickness of 0.050 inch or less.
 12. The golf ball according to claim 1, wherein the cover layer comprises an ionomer, a polyurethane or a polyurea.
 13. The golf ball according to claim 12, wherein the ionomer, polyurethane or polyurea is a castable or reaction injection moldable thermosetting composition.
 14. A golf ball comprising: an inner core comprising a thermoset polybutadiene composition having a first hardness; an intermediate core layer comprising a partially or fully neutralized ionomer having a first vicat softening point temperature and having a second hardness; a heat resistant thermoset layer comprising a theroset material having a second vicat softening point temperature of at least 20° greater than the first and having a third hardness, the thermoset layer comprising a peroxide that decomposes at low temperatures forming free radical initiators with short half lives; and a cover layer.
 15. The golf ball according to claim 14, wherein the intermediate layer has a first vicat softening point temperature of 75° C. or less.
 16. The golf ball according to claim 14, wherein the heat resistant layer has a second vicat softening point temperature of at least 50° C. greater than the first.
 17. The golf ball according to claim 14, wherein the heat resistant layer has a second vicat softening point temperature of at least 100° C. greater than the first.
 18. The golf ball according to claim 14, wherein the first hardness is less than the second hardness, the second hardness is less than the third hardness, and the fourth hardness is less than the third hardness.
 19. The golf all according to claim 14, wherein the peroxide is 1,1-di(t-butylperoxy)cyclohexane, or 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, or 1,1-di(t-amylperoxy)cyclohexane or tbutyl peroxy-(cis-3-carboxy)propenoate.
 20. The golf ball according to claim 19, wherein the peroxide has a half life of less than 10 minutes at 133° C.
 21. The golf ball according to claim 14, wherein the cover layer comprises an ionomer, a polyurethane or a polyurea.
 22. The golf ball according to claim 21, wherein the ionomer, polyurethane or polyurea is a castable or reaction injection moldable thermosetting composition.
 23. The golf ball according to claim 14, wherein the cover layer has a Shore D hardness of less than
 65. 24. The golf ball according to claim 14, wherein the heat resistant thermoset layer comprises polyetheramides; polyetheresters; polyesteramides; thermoplastic urethanes; polyesters such as polybutylene terephthalate or polyethylene terephthalate or copolymers thereof; polycarbonates; polyamides; polypropylene; polyethylene; or mixtures thereof.
 25. The golf ball according to claim 1, wherein the intermediate core layer further comprises of dynamically vulcanized thermoplastic elastomers; suitable functionalized styrene-butadiene elastomers; thermoplastic polyetheresters; polyetheramides; thermoplastic polyesters; or mixtures thereof. 